Process for forming pattern film

ABSTRACT

A process for forming a pattern film comprises irradating a predetermined area of a substrate with an ion beam while simultaneously having present a polymerizable or carbonizable organic compound to thereby polymerize or carbonize the compound upon the area, the compound having a vapor pressure at room temperature of 1×10 -4  to 5×10 -3  Torr. The process is particularly suited for correcting so-called white-spot defects in the manufacture of photomasks.

This is a Rule 62 continuation application of Parent application Ser.No. 706,478 filed Feb. 28, 1985 now abandoned which claims priority ofJapanese Patent Application No. 38131/84 filed Feb. 29, 1984.

BACKGROUND OF THE INVENTION

This invention relates to a process for forming a pattern film for use,for example, in correcting or repairing a photomask during thefabrication of semiconductor devices.

Masks and reticles for use in the manufacture of semiconductors are madeby etching patterns by exposure to light. The process presents problemsbecause of the defects the patterns tend to develop. These defects areclassified into two groups; unwanted pattern portions left unremoved,which are called black-spot defects, and portions needed butunintentionally etched away, called clear or white-spot defects. Ofthese defects, those of the white-spot type are repaired by the use ofan organic compound and irradiation with an ion beam. This has beencarried out in varied ways which have been proposed up to now and whichare broadly of two types.

One typical process consists of applying an organic film, such asphotoresist, to the mask, and then irradiating each portion which has awhite-spot defect with a focused ion beam to thereby polymerize orcarbonize the irradiated portions of the organic film. The film portionpolymerized or carbonized in this manner possesses excellentlight-blocking and adhesion strength properties which render it suitableas a material for correcting white-spot defects. The process hasdrawbacks, however, including the need for the time-consuming step ofapplying the organic film and the necessity of using equipment largeenough to handle the high energy, well in excess of 100 KeV, of thefocused ion beam required for the irradiation.

The other process, developed by the present applicants and described inpublished Japanese Patent Application No. 58-201764 (Laid-Open No.60-94728), involves directing a vapor stream of an organic compound atthe surface of each white-spot defect and concurrently irradiating thesurface with a focused ion beam, whereby the organic compound moleculesare polymerized or carbonized to form a solid deposit on the defectiveportion. The second process has advantages over the first one describedin that it eliminates the separate step of applying an organic film, andthe equipment is simplified because of a lower energy requirement, i.e.,below 30 keV, for the acceleration of the ions needed for irradiation.The kinds or organic compounds thus far proposed for use in knownprocesses of the second type have included vacuum pump oils,organometallic compounds such as trimethylaluminum, and dibenzenecomplexes such as [Cr(C₆ H₆)₂ ].

When vacuum pump oil is used in remedying white-spot defects, its lowvapor pressure at ordinary temperature, i.e., below 10⁻⁶ Torr, makes thesupply of the oil molecules insufficient for film formation bypolymerization or carbonization; consequently, the rate of film buildupto a desired thickness is low. If the vacuum pump oil is heated to raiseits vapor pressure for a faster increase in film thickness, it condenseson the substrate surface. The condensate then gives incompletelypolymerized or cabonized portions along the edges between theion-beam-irradiated and the non-irradiated areas, causing difficulty infilm formation and other undesired effects.

The pattern-film forming processes using organometallic compounds anddibenzene complexes also have drawbacks. When the vapor pressure in thevicinity of the substrate is low, the buildup of the film layerprogresses slowly, and attempts to raise the pressure in order to attainan adequately rapid film buildup will lead to difficulties such as thescattering of the ion beam causing it to go out of focus, an added loadupon the vapor discharge system, and adverse effects upon the ionsource. Furthermore, the organic compounds containing metal atoms whichare typically used are often so toxic or unstable that they posehandling problems.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the difficulties ofthe above-described processes and to provide a means for rapidly forminga pattern film of less than one micron thickness by the use of anorganic compound with good stability and extremely low toxicity.

Thus, the present invention is characterized by the use, as the organicmaterial, of an organic compound having a vapor pressure in the range of1×10⁻⁴ to 5×10⁻³ Torr at ordinary temperature, i.e., room temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of part of a photomask having white-spot defects.

FIGS. 2a and 2b are fragmentary cross-sectional views of part of FIG. 1illustrating the correcting of white-spot defects in a photomask inaccordance with the invention.

FIGS. 3a, 3b and 3c are cross-sectional views illustrating pattern filmformation by using an organic compound according to the invention (FIG.3b) and using organic compounds having vapor pressures at ordinarytemperature of at most 1×10⁻⁴ (FIG. 3a) or at least 5×10⁻³ Torr (FIG.3c).

FIGS. 4a and 4b are photographs of two pattern films which illustratethe process of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, a support plate or substrate 1 of glass or the likehas a pattern film 2 drawn thereon with chromium or other material.Typical kinds of white-spot defects are represented by an area 31 wherethe pattern has been omitted, an interrupted area 32 and a pinhole area33. In this example, the area 31 is non-contiguous with the originalpattern film 2 and the areas 32 and 33 are contiguous with the originalpattern film 2. These white-spot defects, which lead to undesired lighttransmission through the mask, must be corrected, i.e., thelight-transmitting areas need to be treated so that they become asopaque to light as the rest of pattern 2.

In FIG. 2a the areas of omission 31 is corrected in the manner now to beexplained. The numeral 4 designates an ion-beam generator whichcomprises an ion source, such as a liquid metal ion source, and an ionicoptical system for heating, polarizing, and focusing the ions generatedby the source. The ion beam 5 produced by the source is used in scanningthe area of omission 31 to effect ion irradiation at a constant rate.The numeral 6 designates a source which supplies a film-formingdepositable material in the form of an organic compound. The source 6includes a heater that controls the temperature of the source andthereby controls the quantity of vapor 7 of the organic compound to bedelivered to the area 31. In this case, the support plate or substrate 1is at room temperature. The vapor stream 7 of the organic compound, thenature of which will be described later, is deposited predominantly onthe support plate 1. It is polymerized or carbonized by irradiation bymeans of the focused ion beam 5. FIG. 2b shows a pattern film 8 formedin this way in the area of omission 31.

FIG. 3a illustrates a pattern film treated by the use of an organiccompound having a vapor pressure of 1×10⁻⁴ Torr or below at ordinaryroom temperature. In FIG. 3b is shown a pattern film treated with anorganic compound having a room temperature vapor pressure in the rangeof 1×10⁻⁴ to 5×10⁻³ Torr. The conditions employed in using beam 5 forirradiation, the condition of the support plate or substrate 1 and thevapor pressure of the organic compound used in the treatment shown inFIG. 3a are the same as those used in the treatment shown in FIG. 3b. Inthe case illustrated in FIG. 3a, the organic compound deposited on thesupport plate or substrate 1 forms an organic compound layer 9 becauseof its low evaporation rate . The portion of this organic compound layer9 which is irradiated with the focused ion beam in the area 11 isreduced in thickness to a denser solid mass, which is lower in heightthan the original layer 9, and is polymerized or carbonized to form thelocalized pattern film 8. At the same time, areas 10 of incompletelypolymerized or carbonized organic compound develop along the edgesbetween the layer 9 of the organic compound and the pattern film 8.These portions make microfine processing difficult or can becomedetached when the bond strength is insufficient, producing unwantedshadows or causing other problems in the subsequent stage of selectiveexposure of the pattern on a semiconductor wafer.

In the example shown in FIG. 3b, the vapor 7 of an organic compound usedin accordance with the invention and having a room-temperature vaporpressure in the range of 1×10⁻⁴ to 5×10⁻³ Torr was directed against thesurface. The organic compound used according to the present invention,delivered in vapor form onto a localized area of the support plate orsubstrate 1, deposits on the surface, remains there for some time, andthen evaporates. Thus, while the irradiating focused ion beam 5 isscanning, a suitable amount of the organic compound vapor 7 is supplied,and it is polymerized or carbonized by the next scan of the beam. Inthis manner, the localized pattern film 8 grows to a desired thickness.Outside the ion beam scanning area 11 at which the organic compound isalso directed, vapor of the organic compound forms only a negligiblythin layer 9 of the organic compound. Soon after the cutoff of the vaporsupply, the layer 9 will evaporate essentially completely, leavingnothing to interfere with the formation of the pattern film.

In the case of FIG. 3c, the organic compound evaporates immediatelyafter deposition of the support plate 1. Consequently, the volume amountof the organic compound that deposits in the area 11 which is irradiatedwhile the focused ion beam 5 is in its scanning run is too small torealize an adequate rate of film buildup to the desired thickness in theomitted area. In the one example depicted in FIG. 3c, acetylene was usedand the pressure inside the organic gas nozzle was raised to 0.7 Torr.However, ion beam irradiation for as long as 20 minutes did not impartappropriate light-blocking properties to the film.

Suitable examples of film-forming organic compounds suitable for use inaccordance with the invention include tri- or tetracyclic aromaticcompounds such as phenanthrene, pyrene, methylphenanthrene,fluoranthene, anthrone, and triphenylmethane. These organic compoundshave vapor pressures at ordinary temperature in the range of 1×10⁻⁴ to5×10⁻³ Torr. Moreover, they are free from metal, they are stable, andthey are only slightly toxic. Organic compounds other than the tri- andtetracyclic aromatic compounds and having molecular weights of 200 to400 are also useful since their vapor pressures at ordinary temperatureare between 1×10⁻⁴ and 5×10⁻³ Torr.

An example of a pattern film formed from pyrene, selected from among thekinds of organic compounds suitable for use in accordance with thepresent invention, will be described with reference to the illustrationsin FIGS. 4a and 4b. FIG. 4a shows an image obtained by lighttransmission through a sample based on a support plate of clear glassand having a pattern 20 made of a layer of chromium of about 800 Å-thickdrawn thereon yet to be formed with a pattern film in accordance withthe invention. In FIG. 4b there is shown a localized pattern film area20a which is formed according to the process of the invention, measuring6.7 mm by 6.7 μm, on an exposed glass portion of the pattern plate shownin FIG. 4a which is 8 μm square in size. The focused ion beam used forirradiation was formed from Ga⁺, the acceleration voltage was 20 kV, andthe probe current 0.13 nA. The organic compound used was pyrene whichwas heated to 80° C. The pattern film 20a thus formed was 1400 Å thickand provided an adequate shield or block against light transmission,providing the pattern film with sharply defined edges. The rate ofthickness buildup of the pattern film was 69 Å/sec when 200 μm-long linescanning with the Ga⁺ beam was carried out at the acceleration voltageof 20 kV and with the probe current of 0.13 nA. The pattern film widthswere of the order of submicrons. Thus according to the presentinvention, the original pattern 20 is selectively altered by theaddition of the localized pattern film deposit 20a.

The physical and chemical adhesion strengths of the deposited patternfilm produced in this way are about the same as that of the chromiumfilm, the adhesion of which is well known in the art. The thickness ofthe pattern film which provides an optical density of 2.8 wasapproximately 2000 Å for visible light and below 1000 Å for ultravioletrays. Under the aforedescribed film-forming conditions, therefore, it ispossible to form a 200 μm-long, submicron-wide pattern film within 20seconds by exposure of ultraviolet rays. The process of the inventionfor forming a pattern film in the foregoing way is particularly suitedfor producing microfine pattern films. It is also possible, of course,to form a larger area of pattern film at a faster rate by irradiationwith a focused ion beam of a larger diameter with a higher probecurrent.

As has been described in detail above, the present invention permitspattern film formation and localized alteration of pattern films in asingle step that takes only a short period of time and makes possiblemicrofine patterns of less than one micron in width. This makes possiblea substantial reduction in the number of process steps or stagesotherwise required. Further advantages are the ease and which theorganic compound is handled and the possibility of using an apparatus ofsimplified construction.

We claim:
 1. A process for repairing a white-spot defect in the surfaceof a photomask comprising: forming and directing a vapor stream of apolymerizable or carbonizable organic compound onto a surface of aphotomask at the region of a white-spot defect; and irradiating thesurface of the photomask in the region of the white-spot defect with anion beam effective to selectively polymerize or carbonize the organiccompound at the photomask surface in the region of the white-spot defectto thereby repair the white-spot defect.
 2. A process according to claim1; wherein the ion beam comprises a focused ion beam.
 3. A processaccording to claim 1; wherein said organic compound has a saturatedvapor pressure at 300° K. in the range of 1×10⁻⁴ to 5×10⁻³ Torr.
 4. Aprocess according to claim 1; wherein said organic compound has amolecular weight between 200 and
 400. 5. A process according to claim 1;wherein the organic compound is selected from the group consisting oftriacylic and tetracyclic aromatic compounds.
 6. A process according toclaim 2; wherein the focused ion beam comprises a focused Ga⁺ ion beam.7. A process according to claim 1; wherein the organic compound isselected from the group consisting of pyrene, phenanthrene,methylphenanthrene, fluoranthene, anthrone, triphenylmenthane andcombinations thereof.
 8. A process according to claim 2; wherein theirradiating step comprises scanning the focused ion beam over thephotomask surface in the region of the white-spot defect.
 9. A processfor altering the pattern of a pattern film formed on a substrate,comprising the steps of: providing a pattern-filmed substrate having apattern film formed thereon; irradiating a predetermined area of thepattern-filmed substrate with a focused ion beam; and directing a vaporstream of polymerizable or carbonizable depositable material onto alocalized area of the pattern-filmed substrate which is being irradiatedwith the focused ion beam to deposit the depositable material as a filmon the predetermined area of the substrate thereby altering the patternof the pattern film formed on the substrate.
 10. A process according toclaim 9; wherein the irradiating step comprises scanning the focused ionbeam over the predetermined area of the pattern-filmed substrate whilethe vapor stream of depositable material is being continuously directedthereonto so as to control the thickness of the deposited film.
 11. Aprocess according to claim 9; wherein the directing step comprisesdirecting a vapor stream of depositable material comprised ofpolymerizable or carbonizable organic compound.
 12. A process accordingto claim 11; wherein the vapor stream of organic compound has asaturated vapor pressure at 300° K. in the range of 1×10⁻⁴ to 5×10⁻³Torr.
 13. A process according to claim 11; wherein the organic compoundhas a molecular weight between 200 and
 400. 14. A process according toclaim 11, wherein the organic compound is selected from the groupconsisting of tri-acylic and tetracyclic aromatic compounds.
 15. Aprocess according to claim 11; wherein the organic compound is selectedfrom the group consisting of pyrene, phenanthrene, methylphenanthrene,fluoranthene, anthrone, tri-phenylmethane and combinations thereof. 16.A process according to claim 9; wherein the irradiating step comprisesirradiating a predetermined area of the pattern-filmed substrate with afocused ion beam comprised of a focused Ga⁺ ion beam.
 17. A processaccording to claim 9; wherein the providing step comprises providing apattern-filmed substrate comprised of a mask having a white-spot filmdefect; the irradiating step comprises irradiating the mask at apredetermined area thereof at which the white-spot defect appears with afocused ion beam; and the directing step comprises directing a vaporstream of depositable material onto the mask in the localized area ofthe white-spot defect which is being irradiated with the focused ionbeam to deposit the depositable material as a film in the localized areaof the white-spot defect to thereby repair the white-spot defect.
 18. Aprocess according to claim 17; wherein the directing step comprisesdirecting a vapor stream of depositable material comprised ofpolymerizable or carbonizable organic compound.
 19. A process accordingto claim 18; wherein the vapor stream of organic compound has asaturated vapor pressure at 300° K. in the range of 1×10⁻⁴ to 5×10⁻³Torr.
 20. A process according to claim 18; wherein the organic compoundhas a molecular weight between 200 and
 400. 21. A process according toclaim 18; wherein the organic compound is selected fron the groupconsisting of tri-acyclic and tetracyclic aromatic compounds.
 22. Aprocess according to claim 18; wherein the organic compound is selectedfrom the group consisting of pyrene, phenanthrene, methylphenanthrene,fluoranthene, anthrone, tri-phenylmenthane and combinations thereof. 23.A process according to claim 17; wherein the irradiating step comprisesscanning the focused ion beam over the predetermined area of the maskwhile the vapor stream of depositable material is being continuouslydirected thereonto so as to control the thickness of the deposited film.24. A process according to claim 17; wherein the deposited film has awidth of submicron size.
 25. A process according to claim 17; whereinthe irradiating step comprises irradiating a predetermined area of thepattern-filmed substrate with a focused ion beam comprised of a focusedGa⁺ ion beam.
 26. A process according to claim 9; wherein theirradiating and directing steps are carried out to form a deposited filmof submicron size.
 27. A process according to claim 9; wherein theirradiating step comprises irradiating a predetermined area of thepattern-filmed substrate which is non-contiguous with the originalpattern film with a focused ion beam; and the directing step comprisesdirecting a vapor stream of depositable material onto a localized areaof the pattern-filmed substrate which is being irradiated with thefocused ion beam to deposit the depositable material as a film on thepredetermined area of the substrate to thereby form a localizeddeposited film which is non-contiguous with the original pattern film.28. A process according to claim 9; wherein the irradiating stepcomprises irradiating a predetermined area of the pattern-film substratewhich is contiguous with the original pattern film with a focused ionbeam; and the directing step comprises directing a vapor stream ofdepositable material onto a localized area of the pattern-filmedsubstrate which is being irradiated with the focused ion beam to depositthe depositable material as a film on the predetermined area of thesubstrate to thereby form a localized deposited film which is contiguouswith the original pattern film.
 29. A process according to claim 17;wherein the providing step comprises providing a photomask having awhite-spot film defect.
 30. A process according to claim 17; wherein theirradiating step comprises including the mask with a focused ion beamcomprised of a focused beam of positive ions.
 31. A process according toclaim 30; wherein the focused beam of positive ions comprises a focusedbeam of positive metallic ions.
 32. A process according to claim 9;wherein the irradiating step comprises irradiating the pattern-filmedsubstrate with a focused ion beam comprised of a focused beam ofpositive ions.
 33. A process according to claim 32; wherein the focusedbeam of positive ions comprises a focused beam of positive metallicions.